The present invention relates to a method for operating a metering valve for introducing a urea-water solution into the exhaust train of an internal combustion engine, and it also relates to a method for operating an internal combustion engine having a charge air cooler and a metering valve.
In an internal combustion engine, for example, the internal combustion engine of a passenger car or a truck, the internal combustion engine can give rise to high temperatures on the internal combustion engine itself as well as on components of the internal combustion engine, for example, in the exhaust train of the internal combustion engine, and these temperatures can destroy or damage parts and components in the areas exposed to these temperatures.
German patent application DE 10 2009 014 361 A1 relates, for example, to an exhaust-gas treatment unit for a vehicle with an SCR catalytic converter for reducing nitrogen oxides in the exhaust gas of an internal combustion engine. A turbocharger is installed upstream from the SCR catalytic converter. A metering unit serves to introduce a reductant into the exhaust gas at a feed site that is preferably arranged upstream from a turbine of the turbocharger. The metering unit can be actuated by means of a control unit, whereby it can also be provided that an aqueous urea solution is introduced into the exhaust gas system if very high exhaust-gas temperatures would otherwise lead to severe thermal stress to the turbine. In this case, aside from the need to reduce nitrogen oxide, the introduction of the aqueous urea solution can be provided as a measure to protect against temperatures at which exhaust gases cool off due to the application of evaporation heat.
In the case of supercharged engines, for example, turbo-engines, charge air coolers are used in order to ensure that air heated up by the supercharging is cooled off, as a result of which a higher charging density is made available to the combustion process in the cylinder. In conjunction with a low-pressure exhaust gas recirculation system, exhaust gases are introduced into the compressor together with the intake air. The compressed charge air is conveyed through the charge air cooler and it is finally fed to the combustion process after having been cooled off to a considerable extent. During the operation of such a low-pressure exhaust gas recirculation system, the water contained in the exhaust gas can condense in the charge air cooler and, if it accumulates, it can damage the charge air cooler and the internal combustion engine. In this context, German patent application DE 10 2009 006 966 A1 relates to a method for regulating the charge air cooler that is located in a coolant circuit of an internal combustion engine and that cools the charge air of the internal combustion engine. Here, the cooling capacity of the charge air cooler is set by means of an adjustable circulation pump. German patent application DE 10 2008 035 747 A1 relates to an exhaust gas recirculation cooling system having several coolers. In order to avoid the formation of deposits on the cooler, so-called fouling (overcooling and condensation), the exhaust gas recirculation flow through and around several coolers is coordinated as a function of the operating conditions.
German patent application DE 10 2007 038 242 A1 relates to a method for recirculating exhaust gas in order to feed the largest possible portion of exhaust gas that has been thoroughly mixed with fresh air back to an internal combustion engine at all of the operating points while reliably avoiding condensation effects. For this purpose, the portion of exhaust gas that is removed from the outlet line and fed back in upstream from a compressor in the inlet line is controlled and regulated as a function of the temperature in the inlet line.
Finally, German patent application DE 10 2009 006 966 A1 relates to a method for regulating a charge air cooler with which the cooling capacity of the charge air cooler is set during the operation of the internal combustion engine as a function of two threshold values for the temperature of the charge air cooler. The cooling capacity of the charge air cooler can be set, for instance, by means of an adjustable circulation pump. In this manner, it is possible to lower the inertia of the cooling system.
In the case of a supercharged internal combustion engine, for example, a diesel engine with a turbocharger, in order to treat the exhaust gas, a urea-water solution (HWL) can be injected into the exhaust train, for example, upstream from an SCR catalytic converter (SCR=selective catalytic reduction) and upstream from a diesel particulate filter (DPF) via a metering valve, a so-called SCR metering valve. Depending on the installation position of the metering valve in the exhaust train of the internal combustion engine, the metering valve can be exposed to very high temperatures.